1. Field of the Invention
The present invention relates to a method and apparatus for scanning a light beam on a workpiece such as semiconductor substrate in an XY plane and, in particular, to an inexpensive and cost effective method and apparatus for laser scanning in an XY raster pattern.
2. Description of Related Art
Scanning systems using light and in particular lasers, are employed in many applications. For example, scanning lasers are used in laser printers and to drill holes in a semiconductor substrate to create micro-circuitry, scribe alpha-numerics on a container or part, read bar codes, marking, expose, stenciling, patterning and other related laser or light processes. The goal of scanning is to cover in an XY plane an area with a light source in a systematic and expedient manner and includes both coherent and non-coherent sources such as a laser and an illuminator light source. For convenience, the following description will be directed specifically to lasers since these are the most used systems, however, it will be appreciated by those skilled in the art that the invention could be used for other light sources and for all types of laser systems such as Nd:YAG and HeNe laser systems.
There are various methods and apparatus used today to laser scan an object or mask work piece. These include Galvanometers, servo controlled mirrors, polygon scanners and the like to position the laser beams. In general, before the beam is completely focused it passes through a scanning mechanism which provides the means to scan the beam on a mask plane or work piece bi-directionally. The scanned beam then passes through the mask plane, through an objective lens and onto the work piece substrate
One commercial laser scanning apparatus uses post-objective scanning technology comprising a pair of rugged, position-feedback, moving iron Galvanometers with engineered mirrors, optimized for precise positioning of laser beams along the XY axes. A computer in the scanner computes all flat field scan correction and directs vector scan movements on the work piece. Raster scanning can be simulated defining link parallel vector movements. A lower cost optical Galvanometer scanner does not include a positioned sensor to provide feedback for precise positioning and is intended primarily as a lower cost alternative where speed or response or accuracy is not required. Typical applications include facsimile transmissions and optical pointing or tracking.
Scanning systems to be effective must be flexible for various scan speeds, spot sizes, Y-axis indexing and X-axis scans at the object plane and current systems used to perform such XY scanning are complex and expensive.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an apparatus and a method for laser scanning an object in an XY plane which is inexpensive and cost effective.
A further object of the invention is to provide an improved method and apparatus for laser scanning in which various scan speeds, spot sizes, Y-axis indexing and X-axis scans can be easily and effectively used.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.